Use HttpClient in PictureBox

[lonitra]

ServicePointManager and WebClient are obselete, but are being used in PictureBox

winforms/src/System.Windows.Forms/src/System/Windows/Forms/Controls/PictureBox/PictureBox.cs

Lines 500 to 524 in 520c319

	private void LoadImageViaWebClient()
	{
	Image img;
	Uri uri = CalculateUri(_imageLocation!);
	if (uri.IsFile)
	{
	_localImageStreamReader = new StreamReader(uri.LocalPath);
	img = Image.FromStream(_localImageStreamReader.BaseStream);
	}
	else
	{
	if (LocalAppContextSwitches.ServicePointManagerCheckCrl)
	{
	ServicePointManager.CheckCertificateRevocationList = true;
	}
	#pragma warning disable SYSLIB0014 // Type or member is obsolete
	using WebClient webClient = new(); // lgtm[cs/webrequest-checkcertrevlist-disabled] - Having ServicePointManager.CheckCertificateRevocationList set to true has a slim chance of resulting in failure. We have an opt-out for this rare event.
	#pragma warning restore SYSLIB0014 // Type or member is obsolete
	_uriImageStream = webClient.OpenRead(uri.ToString());
	img = Image.FromStream(_uriImageStream);
	}
	InstallNewImage(img, ImageInstallationType.FromUrl);
	}

We needed to suppress SYSLIB0014 warning in #11540 to unblock depdency flow, but we should update this code to use HttpClient

[paul1956]

PR #11215 provides a webserver for testing HTTP client downloads.